This invention relates to filament winding wherein a plurality of filaments or strands are wound onto a workpiece or mandrel. More particularly, this invention relates to apparatus for feeding and winding strands of preimpregnated fibrous composite material about a mandrel.
Various articles are manufactured by winding strands or filaments that are impregnated with a resin onto a rotating mandrel that corresponds to the shape of the article being fabricated. When the filament winding process is complete, the article is cured and the mandrel is removed. In the type of winding process to which this invention is primarily directed, a feed system gathers a plurality of individual strands into a side-by-side relationship to supply a band of strands that is wound about the rotating mandrel so as to form a number of superposed, helically wound layers. In addition, the invention is primarily directed to a filament winding system that employs preimpregnated fibrous strands. As is known in the art, preimpregnated strands (or "prepreg") consist of anisotropic fibers (such as graphite) that have been impregnated with a thermosetting or thermoplastic resin and heated to cause fusing of the fiber layers into a substantially unitary article.
The feed systems employed in prior art filament winding arrangements typically include a combination of guide elements such as combs and rollers that control the strands as the strands are drawn from individual supply spools, brought into spacedn-apart alignment with one another, and collimated within a feed eye to form a substantially uniform band for winding onto the rotating mandrel. There are several disadvantages and drawbacks to such prior art feed systems when preimpregnated strands are employed. Firstly, in many of the prior art systems, the strands are subjected to substantial impact and frictional contact with the various guide elements. This impact and frictional contact often causes fraying or other strand damage. Secondly, in prior art filament winding systems, the strands often tend to twist or bunch as they pass through the feed eye, rather than forming the desired substantially flat band. Both fiber damage and distortion of the filament band can substantially affect the structural integrity and strength of the article being fabricated. In addition, prior art feed eyes are generally curved or annular components that are commonly constructed of graphite, glass, nylon or steel. In many cases, friction between the feed eye and the passing band of composite material causes excessive feed eye wear and/or heats the feed eye to a temperature that melts the resin that impregnates the strands. When excessive resin melting occurs, the resin often accumulates and collects particles that are dislodged from the strands as they pass through the feed eye. This accumulated melted resin and particles often dislodge and are carried into the mandrel windings. Excessive feed eye wear results in grooves that tend to damage the passing strands and, in some instances, the strands become contaminated with particles of the feed eye material. Both of these conditions can seriously affect the quality of the article being fabricated.